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app/providers.tsx

@@ -2,7 +2,27 @@
 
 import { SessionProvider } from "next-auth/react";
 import type { ReactNode } from "react";
+import { useEffect } from "react";
 
 export default function Providers({ children }: { children: ReactNode }) {
+  useEffect(() => {
+    if (typeof document === "undefined") return;
+    const root = document.documentElement;
+    const applyTheme = () => {
+      try {
+        const saved = window.localStorage.getItem("theme");
+        if (saved === "dark" || saved === "light") {
+          root.dataset.theme = saved;
+        }
+      } catch {
+        // ignore
+      }
+    };
+    applyTheme();
+    const handler = () => applyTheme();
+    window.addEventListener("storage", handler);
+    return () => window.removeEventListener("storage", handler);
+  }, []);
+
   return <SessionProvider>{children}</SessionProvider>;
 }